Defending champion Isner - the world number 12 - accounted for Sock in straight sets on Saturday to keep him on track for back-to-back successes on the Atlanta hard courts.
Isner, who overcame South African Kevin Anderson in last year's decider after consecutive runner-up finishes in 2010 and 2011, won 94 per cent of his first service points in 97 minutes on court.
The towering American also won two break points against his practice partner, who is now 4-1 in arrears in their head-to-head standings.
"It was not easy conditions at all in the heat today," said Isner, who avenged his quarter-final loss to Sock in Newport a fortnight ago.
"I thought I played pretty well. Jack is a really good player. I wanted to win that match."
Isner will now face Dudi Sela in the final after the Israeli prevailed 6-3 3-6 6-3 against Benjamin Becker in Saturday's other semi.
Sela - whose only other ATP career final was in Beijing when he lost to Andy Roddick in 2008 - was on court for almost two hours before defeating the German for the first time in his career, having lost the two previous meetings.
The 29-year-old fired down three aces and saved five break points.
"I feel great [being in the final]. The atmosphere is great here in Atlanta," said Sela after the match.
"The crowd support was incredible."